Tropical Depression Pewa dissipated in the northwestern Pacific Ocean early on Aug. 26, 2013. NASA satellite data on the previous day showed that rainfall had greatly diminished in the depression.

On Aug. 25, Tropical Depression Pewa's circulation had expanded and the storm weakened. Forecasters at the Joint Typhoon Warning Center expected Pewa would dissipate over the next day. Earlier thoughts were that Pewa might hang together and become an extra-tropical storm, but it appears that the life is leaving the storm.

The Joint Typhoon Warning Center's official, final position for Pewa was noted on Aug. 25 at 0300 UTC/Aug. 24 at 11 p.m. EDT, when it was centered near 28.7 north and 166.5 east. It was about 552 nautical miles north of Wake Island and was moving west-northwest at 8 knots/9.2 mph/14.8 kph.

NASA's TRMM/Tropical Rainfall Measuring Mission satellite captured Pewa's waning rainfall on Aug. 25 at 14:17 UTC/10:17 a.m. EDT. TRMM's precipitation radar data showed moderate rainfall in a small area in the southwestern quadrant of the depression. At that time, most of the system either had light rain or is rain-free. By Aug. 26, Pewa passed in the Pacific.

Cloud top temperatures warmed up on NASA infrared imagery, indicating that the uplift in Tropical Storm Pewa was waning. By Aug. 23, Pewa was reduced to a tropical depression. Infrared imagery also showed that wind shear has pushed Pewa's precipitation away from the storm's center.

On Aug. 22 at 01:35 UTC (2:53 p.m. EDT) NASA's Atmospheric Infrared Sounder or AIRS instrument that flies aboard NASA’s Aqua satellite showed a limited area of cloud top temperatures in bands of thunderstorms east of the center of Tropical Depression Pewa were as cold as -63F/-52C, indicating strong storms. Satellite data indicated that Pewa's low-level circulation center is partially exposed to outside winds and wind shear continues to push the bulk of precipitation east of the center.

AIRS infrared images are false-colored to show temperature differences. Scientists look at cloud top temperatures to understand how high the thunderstorms are that make up a tropical cyclone - and there are hundreds of thunderstorms that make up one storm. The colder the cloud top temperature, the higher the top of the thunderstorm reaches into the troposphere and the stronger the storm. NASA research has indicated that cloud top temperatures that reach or exceed the threshold of -63F/-52C typically have heavy rainfall rates.

On Aug. 23 at 1500 UTC/11 a.m. EDT Tropical Depression Pewa's maximum sustained winds had fallen to 30 knots/34.5 mph/55.5 kph. Pewa was centered near 26.9 north and 168.5 east, about 458 nautical miles northeast of Wake Island. Pewa is moving to the northeast at 4 knots/4.6 mph/7.4 kph. Forecasters at the Joint Typhoon Warning Center expect Pewa to turn back to the northwest and continue on a northerly track over open ocean.

The Joint Typhoon Warning Center noted that Pewa is expected to struggle over the next several days is it moves in a northerly direction. Pewa is also expected to become extra-tropical over the next couple of days.

A view of the Pacific Ocean from NOAA's GOES-West satellite caught Tropical Storm Pewa moving through the Northwestern part of the ocean and two developing low pressure areas, one designated System 94E, several hundred miles off the Mexican coast.

NOAA's GOES-West satellite infrared imagery from today, Aug. 22 at 1200 UTC/8 a.m. EDT showed Tropical Storm Pewa heading west in the Northwestern Pacific. Pewa had a rounded circulation. The other two developing lows did not appear circular in the GOES-West image. The GOES image was created by the NASA GOES Project at NASA's Goddard Space Flight Center in Greenbelt, Md. Multi-spectral satellite imagery revealed that the convection is still shallow (weak) on the western side of the tropical storm, but convection is stronger over the center of circulation.

At 0900 UTC/5 a.m. EDT on Aug. 22, Pewa was centered near 23.6 north latitude and 169.3 west longitude, about 280 nautical miles northeast of Wake Island. Maximum sustained winds are near 35 mph/55 kph. Tropical Storm Pewa is moving to the north-northwest at 11 knots/12.6 mph/20.3 kph and the Joint Typhoon Warning Center expects it to continue moving in that direction for the next couple of days. Pewa is headed into cooler waters over the next several days, which are expected to slowly weaken the system, according to the Joint Typhoon Warning Center

The broad area of low pressure, which does not have an investigation number yet, appears disorganized on the GOES-West satellite imagery. The low is located near 16 north and 122 west, about 900 miles southwest of the southern tip of the Baja California peninsula. The low continues to generate limited shower and thunderstorm activity and the National Hurricane Center expects the low to become absorbed into the circulation associated with System 94E. As System 94E organizes and strengthens, this low pressure area's chances for developing into its own depression have dwindled to just 10 percent.

System 94E is the low pressure area to watch in the Eastern Pacific. It has high chance for becoming a tropical depression later today, Aug. 22, or tonight. It is centered about 425 miles south of Cabo San Lucas, Mexico. The National Hurricane Center noted that during the morning hours on Aug. 22, showers and thunderstorms have re-formed near the center. The low is expected to move north-northwestward at 5 to 10 mph and reach colder water west of the Baja California peninsula by the weekend of Aug. 24 when conditions will not favor development.

Pewa is expected to strengthen a little over the next several days before it weakens, while System 94E will likely become a new tropical depression in the Eastern Pacific over the same time frame.

Tropical Storm Pewa continues trekking through the open waters of the Northwestern Pacific Ocean today, and was captured on NASA satellite imagery.

On Aug. 21 at 1500 UTC, Tropical Storm Pewa had maximum sustained winds near 35 knots/40.2 mph/64.8 kph. Pewa is a small storm, and tropical-storm-force winds extend from the center up to 65 miles. It was centered near 20.9 north latitude and 170.4 east longitude, about 242 nautical miles/278.5 miles/448.2 km east-northeast of Wake Island.

Wake Island is a coral atoll. Its coastline stretches only 12 miles/19 km and it is located just north of the Marshall Islands. Pewa continues moving past Wake Island in a north-northwesterly direction at 12 knots/13.8 mph/22.2 kph.

NOAA's GOES-West satellite captured an image of Pewa on Aug. 21 at 1500 UTC/11 a.m. EDT. GOES-West imagery is created at the NASA GOES Project at NASA Goddard Space Flight Center in Greenbelt, Md. The GOES-West satellite data showed Pewa still has bands of thunderstorms around the center and northern quadrant of the circulation.

Pewa is expected to intensify again while moving northwest. The Joint Typhoon Warning Center forecast indicates that it is expected to become a typhoon over the next five days.

The Atmospheric Infrared Sounder or AIRS instrument aboard NASA's Aqua satellite captured an infrared image of Tropical Storm Pewa on Aug. 20 at 01:47 UTC/9:47 p.m. EDT, Aug. 19 as it weakened. The coldest cloud top temperatures and strongest storms were confined to a small area around the storm's center and in a band of thunderstorms northeast of the center. Cloud top temperatures in both of those areas were as cold as -63F/-52C. Infrared imagery since this AIRS image has shown that convection has deepened and thunderstorms have become stronger.

At 0900 UTC on Aug. 20, Pewa's maximum sustained winds dropped to 45 knots/51.7 mph/83.3 kph as it faced wind shear. By 1500 UTC/11 a.m. EDT, winds had strengthened to 50 knots/57.5 mph/92.6 kph. Forecasters at the Joint Typhoon Warning Center expect Pewa to strengthen into a typhoon later this week. Pewa was located near 17.5 north and 173.4 east, about 436 nautical miles east-southeast of Wake Island. Pewa is moving to the northwest at 13 knots/15 mph/24 kph and is expected to pass far to the north of Wake Island from Aug. 21 to 22.

Forecasters at the Joint Typhoon Warning Center noted that as Pewa moves through warm ocean waters, a decrease in vertical wind shear will happen over the next couple of days and that will allow for Pewa to strengthen to typhoon force.

NASA's Aqua satellite passed over the tropical cyclone known as Pewa after it strengthened into a typhoon in the northwestern Pacific Ocean. The Aqua satellite image revealed that Pewa had developed a small eye.

On Sunday, Aug. 18, Pewa was a tropical storm when it crossed the International Date Line and moved from the Central Pacific to the Northwestern Pacific Ocean. Pewa now falls under the forecast authority of the Joint Typhoon Warning Center.

On Aug. 18, infrared satellite data showed that thunderstorm development and convection had slightly weakened, but the system remained well-organized. Forecasters at the Joint Typhoon Warning Center or JTWC, expected the slight weakening to quickly reverse itself as conditions around the storm improved. The JTWC forecast that Pewa would become a typhoon on Aug. 19, and it did.

NASA's Aqua satellite passed over Typhoon Pewa on Aug. 19 at 01:05 UTC shortly after it strengthened into a typhoon in the northwestern Pacific Ocean. The Moderate Resolution Imaging Spectroradiometer instrument image showed that Pewa developed a small eye surrounded by strong thunderstorms.

On Monday, Aug. 19 at 0900 GMT/5 a.m. EDT, Typhoon Pewa had maximum sustained winds near 65 knots/75 mph/120 kph. It was centered near 13.9 north and 177.9 east, about 726 nautical miles east-southeast of Wake Island. Pewa was moving to the northwest at 8 knots/9.2 mph/15 kph.

Pewa is expected to continue to intensify as it moves northwest. The JTWC expects Pewa to pass far to the northeast of Wake Island on Aug. 21 and 22.

NASA's Aqua satellite passed over two developing low pressure areas in the Central Pacific Ocean, just before one of them strengthened into Tropical Storm Pewa.

When NASA's Aqua satellite passed over the Central Pacific on Aug. 16 at 00:35 UTC (8:35 p.m. EDT/Aug. 15), the Moderate Resolution Imaging Spectroradiometer or MODIS instrument captured a visible image of two developing low pressure areas. The low farthest west was called System 91C, and that's the low that strengthened into Tropical Storm Pewa. The low pressure area east of Pewa is System 90C, which has a high chance to develop into a tropical depression.

System 90C is located near 12.6 north and 163.5 west, which is about 775 miles south-southwest of Kauai, Hawaii. System 90C is moving west near 15 mph.

NOAA's Central Pacific Hurricane Center or CPHC noted that outflow from Tropical Storm Pewa is adversely affecting System 90C's chances for developing further. Satellite imagery early on Aug. 16 showed that System 90C appears less organized than it did on Aug. 15. This system has a medium chance, 30 percent, of becoming a tropical cyclone during the next 48 hours.

There's another low pressure area east of System 90C, but it has a "near zero" percent chance of development. The area is actually a trough or elongated area of low pressure, and has not been given a system designation. It is producing disorganized showers and thunderstorms and was moving west at 15 to 20 mph. Because environmental conditions are not favorable, this low is not likely to become a tropical depression in the near future, according to CPHC.

On Aug. 16 at 1500 UTC/11 a.m. EDT/5 a.m. Hawaii Standard Time, Tropical Storm Pewa's maximum sustained winds were near 40 mph/65 kph. Pewa was centered near 10.2 north and 173.5 west, more than 1,250 miles southwest of Kauai, Hawaii. Pewa is moving to the west-northwest at 15 mph. The Central Pacific Hurricane Center forecast for Pewa takes the storm on a northwesterly track with its center staying over open ocean. Pewa is expected to maintain tropical storm status for the next several days.

This infrared image from NASA’s Aqua satellite on Aug. 22 at 01:35 UTC showed a limited area of cloud top temperatures of thunderstorms east of the center of Tropical Storm Pewa were cold as -63F/-52C (purple) indicating strong storms.

Image Credit:

NASA/JPL

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On Aug. 25, NASA's TRMM Satellite precipitation radar data showed moderate rainfall in a small area in the southwestern quadrant of Tropical Depression Pewa as it continued to weaken.